A semiquantitative culture technic for identifying infection due to steel needles used for intravenous therapy

Using steel intravneous needles obtained from patients with hematologic malignancies, the authors evaluated the efficacy of a semiquantitative method for culturing vascular cannulas on solid medium, comparing it with conventional broth culture. Of 148 needles studied, 140 (95%) were negative on semiquantitative culture (less than 15 colonies on the plate) although 38 produced growth in broth or on the plate; none of these needles caused septicemia. Eight needles were positive on semiquantitative culture (greater than or equal to 15 colonies), and two of these caused septicemia (P = .002). Positive semiquantitative cultures were associated with local inflammation (P = .02). Semiquantitative culturing was equal to the broth method in sensitivity (100%) in the diagnosis of needle-related septicemia; specificity (96% vs. 92%) and the predictive value of a positive needle culture (25% vs. 14%) were both enhanced with the semiquantitative method. The semiquantitative technic differentiates infection from contamination and offers other major advantages compared with the broth method, and is recommended for culturing steel needles as well as plastic catheters.